Evaluation of Effectiveness of PFS Method Using 3D Finite ...
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Proceedings of the First International Conference on Press-in Engineering 2018, Kochi - 209 - Evaluation of Effectiveness of PFS Method Using 3D Finite Element Method Keisuke TANAKA Engineer, Kajima Corporation, Tokyo, Japan Makoto KIMIZU Engineer, Takahara Wood, Yatsushiro, Japan Jun OTANI Professor, X-Earth Center, Kumamoto University, Japan Email: [email protected] Teruo NAKAI Professor Emeritus, Nagoya Institute of Technology, Japan ABSTRACT In order to improve the effectiveness of steel sheet-pile method for the countermeasure on soft ground settlement under embankment load, a PFS method was developed under the research group whose chair was Prof. Ochiai of Professor Emeritus at Kyushu University, Japan in 2005. At that moment, a series of in-situ full scale tests for this countermeasure method including PFS method which is the combination of end bearing sheet-pile with those of floating type were conducted in the City of Kumamoto, Japan under the Ministry of Construction (current name of this ministry is Ministry of Land, Infrastructure, Transportation and Tourism). In this paper, the main objective is to discuss the quantitative evaluation of PFS method using coupling finite element analysis. Because of the geometry of PFS structures, this analysis was conducted in three dimensions. A numerical analysis was done for the cases of the full scale tests at the site in Kumamoto City, in which the field tests with the case of PFS method was conducted. A “tij model” developed by Nakai et al which can be considered the effect of intermediate principal stress was used as a constitutive model for clayey soil. Here, not only displacements in the ground but also the change of excess pore water pressure were compared. Finally, based on those numerical studies, an effectiveness of PFS method as a countermeasure method was discussed. Key words: Steel sheet-pile, Soft soils, Countermeasures, Numerical Method, Elastoplastic 1. Introduction Steel sheet-pile has been widely used, especially for earth retaining or excavation. In those cases, the reduction of lateral displacement with its total stability has been expected and the installation of the sheet-pile is relatively easy, so that most of those works have been realized as a temporally ones. However, recently this sheet-pile method is being used as a permanent method for the prevention technique on slope failures, and that for the case of embankment construction, the sheet-pile has been constructed at the toe of embankment due to the purpose of stress shut down to the surrounding ground, so that the reduction of subsidence is expected at the area where the private housings are located. When the embankment is constructed on soft ground, the ground subsidence for not only the ground under the embankment but also the ones around embankment are serious problems and some countermeasures have to be considered. A steel sheet-pile method is one of the countermeasures for this problem as shown in Fig. 1. However, this type of structure has a cost problem when the area and depth of soft ground are wider and deeper,
Transcript of Evaluation of Effectiveness of PFS Method Using 3D Finite ...
Proceedings of the First International Conference on Press-in Engineering 2018, Kochi
- 209 -
Evaluation of Effectiveness of PFS Method Using 3D Finite Element Method
Keisuke TANAKA
Engineer, Kajima Corporation, Tokyo, Japan
Makoto KIMIZU
Engineer, Takahara Wood, Yatsushiro, Japan
Jun OTANI
Professor, X-Earth Center, Kumamoto University, Japan
Email: [email protected]
Teruo NAKAI
Professor Emeritus, Nagoya Institute of Technology, Japan
ABSTRACT
In order to improve the effectiveness of steel sheet-pile method for the countermeasure on soft ground settlement under
embankment load, a PFS method was developed under the research group whose chair was Prof. Ochiai of Professor
Emeritus at Kyushu University, Japan in 2005. At that moment, a series of in-situ full scale tests for this countermeasure
method including PFS method which is the combination of end bearing sheet-pile with those of floating type were
conducted in the City of Kumamoto, Japan under the Ministry of Construction (current name of this ministry is Ministry
of Land, Infrastructure, Transportation and Tourism).
In this paper, the main objective is to discuss the quantitative evaluation of PFS method using coupling finite element
analysis. Because of the geometry of PFS structures, this analysis was conducted in three dimensions. A numerical
analysis was done for the cases of the full scale tests at the site in Kumamoto City, in which the field tests with the case
of PFS method was conducted. A “tij model” developed by Nakai et al which can be considered the effect of
intermediate principal stress was used as a constitutive model for clayey soil. Here, not only displacements in the
ground but also the change of excess pore water pressure were compared.
Finally, based on those numerical studies, an effectiveness of PFS method as a countermeasure method was discussed.
Key words: Steel sheet-pile, Soft soils, Countermeasures, Numerical Method, Elastoplastic
1. Introduction
Steel sheet-pile has been widely used, especially for
earth retaining or excavation. In those cases, the reduction
of lateral displacement with its total stability has been
expected and the installation of the sheet-pile is relatively
easy, so that most of those works have been realized as a
temporally ones. However, recently this sheet-pile method
is being used as a permanent method for the prevention
technique on slope failures, and that for the case of
embankment construction, the sheet-pile has been
constructed at the toe of embankment due to the purpose
of stress shut down to the surrounding ground, so that the
reduction of subsidence is expected at the area where the
private housings are located. When the embankment is
constructed on soft ground, the ground subsidence for not
only the ground under the embankment but also the ones
around embankment are serious problems and some
countermeasures have to be considered. A steel sheet-pile
method is one of the countermeasures for this problem as
shown in Fig. 1. However, this type of structure has a cost
problem when the area and depth of soft ground are wider
and deeper,
Proceedings of the First International Conference on Press-in Engineering 2018, Kochi
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so that a development of new sheet-pile method was
expected.
In 1975, a collaborative study was started between
Kyushu University and the Ministry of Construction
(Ministry of Land, Infrastructure, Transportation and
Tourism at present) in Japan. Under this collaboration, a
series of in-situ full scale tests were conducted in Kyushu
area. Based on those activities, a research committee for
developing a new sheet-pile method was established in
2003 in which the chair was Prof. Hidetoshi Ochiai,
Professor Emeritus of Kyushu University, Japan. In 2005,
a new sheet-pile method called PFS method (Partial
Floating Sheet-pile) was proposed under the activities of
this committee. In this method, the end bearing sheet-pile
and that of floating type were combined to deal with its
effectiveness and cost as shown in Fig. 2. Fig. 3 shows
the details of this structure (PFS Method, Technical
Manual, 2005).
In this paper, first of all, in-situ measurements at the
site is introduced as a performance of PFS method and
then, a numerical modeling using 3D FEM is conducted
for one of the PFS construction sites. Finally, based on
the results shown in this paper, the effectiveness of PFS
method is convinced and the next step on this PFS
method is briefly discussed.
2. Case history
A large number of in-situ full scale tests for PFS
Fig. 1 Sheet-pile countermeasures
(a) Without countermeasures
Soft ground
(consolidation) Bearing stratum
Embankment
(b) With sheet-pile countermeasures
Sheet pile
Bearing stratum
Embankment
(a) Conventional type (b) Floating type
(c) (a)+(b)
Effectiveness: high
Cost : high
Effectiveness: low
Cost : low
Soft ground (consolidation)
Effectiveness: high
Cost : low
Fig. 2 Idea of PFS method
Floating Sheet pile
Soft ground
End bearing Sheet pile
Fig. 3 PFS method
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method were conducted in Kumamoto City, Japan. This
area is well known as a region of Ariake clay which is
highly sensitive clay and its depth is up to 40m. Fig. 4
shows the soil profile at the site of in-situ test for PFS
method. In this case, one end bearing sheet-pile for five
floating sheet piles were constructed. Fig. 5 shows the
results of measurement for the settlements at the site and
Fig. 6 shows the results of lateral displacement at the toe
of embankment. As easily realized, the effectiveness of
the PFS method is clearly shown. Since a large volume of
sheet-pile materials were reduced, the cost of the PFS
method is obvious and the construction time is also highly
reduced because of the less volume of the sheet-piles.
3. Numerical analysis
3.1. Site condition
A series of numerical modeling were conducted for
one of the site of PFS method. First of all, the
information at the site in Kumamoto City, Japan is shown
in Fig. 7, in which the height of embankment was 4m
with 48 m width and the total length of the sheet-pile for
end bearing was 30m while the floating part was 20m.
The embankment was constructed by step by step
loadings with total of 40 days as shown in Fig. 8. Fig. 9
shows the soil condition, which is the multi-layer of sand
and Ariake clay. In fact, the layers of Ac1, Ac2-U and
Ac2-L were relatively soft clayey soils and the water
level was relative shallow as 0.8m depth. It is obvious
that total depth of the ground (H=25m) is mostly soft soil
with SPT N-value of nearly zero.
3.2. FEM modeling
Based on the results of soil tests at the site and
laboratory for the soils at the site, all the soil parameters
were determined as shown in Table 1, in which the sandy
ground was assumed as an elastic material while tij model
(Nakai, 2013) was used for clayey ground. An
elasto-plastic consolidation analysis was conducted with
Finite Element Method (FEM) and here, because of the
shape of PFS method, three dimensional analysis was
conducted. Fig. 10 shows the 3D mesh with those scaling
for this analysis in which the total number of elements is
4550 for the ground. Sheet-pile was modeled by beam
Embankment Clayey soil Sandy
soil Clayey soil
Clayey soil
Clayey soil Sandy
soil
Floating
Sheet pile
L=19.5m
End bearing
Sheet pile
L=34.5m One end bearing Sheet pile for five Floating
Sheet piles
4.0m
Fig. 4 Ground condition at the site
27.5m
支持層
軟弱層
盛土
48m
30m
20m
2m8m
Fig. 7 PFS method at the site
4.0m
After 4 years
and 1months Set
tlem
ent
(mm
)
Embankment
Fig. 5 Measurement results of subsidence at
the ground surface
0
Fig. 6 Measurement results of lateral displacement at
the toe of embankment
Proceedings of the First International Conference on Press-in Engineering 2018, Kochi
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elements in which joint element was not used for the
interaction behavior. And in the analysis, the step of
embankment during construction was modeled by adding
solid elements with its weight based on the loading
process as shown in Fig. 8. In the analysis, the results such
as total settlement at the center of the embankment with
that of each soil layer and the change of excess pore water
pressure were calculated.
3.3. Results and discussion
Fig. 11 shows the comparison between numerical
results with those of observations at the site for
settlements. Here, total settlement and those of 3
different clayey layers were compared. As easily realized
from those figures, the numerical results can simulate
real behaviors relatively well. Fig. 12 also shows the
same type of comparison for excess pore water pressure
for different soil layers (Ac1, Ac2-U, Ac2-L, and As2).
Although there are some difference between analysis
results and those of measurements, especially just after
the end of embankment, it can be said that over all
behavior seems close enough for both results. Fig. 13
shows the comparison between numerical results with
those observations for the distribution of lateral
displacement at the toe of the embankment after 250 days.
As shown those comparisons, the numerical results can
simulate real behavior to some extent and as a result, 3D
FEM with elasto-plastic constitutive model by tij model
can model the real behavior, fairly well.
4. Concluding remarks
In this paper, the numerical analysis on the PFS
method was compared with the measurement results at
the site and fairy good agreements were obtained.
However, the location of the site of full scale test is
limited, so that the performance of PFS method with
different soil conditions have to be checked. In fact, one
of the important requirement for the use of steel pile is
0
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3
4
5
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7
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0 50 100 150 200 250
8
6
4
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00 50 100 150 200 250
経過時間(day)
盛土施工高
(m)
Elapsed time (day)
Em
ban
km
ent
hei
gh
t (m
)
Fig. 8 Loading step at the site for FEM
支持層
軟弱層
盛土
48m
30m
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m
2m8m
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盛土施工高
(m)
34m
42m24m
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X
YZ
盛土PFS工法
軟弱地盤
0
3.14.6
8.09.4
17.2
23.0
24.4
30.0
深さ(m) N値0 10 20 30
B
Ac1Am1
Dg1
Am2
As1
As2
Ac2-L
Av
Ac2-U
Dc1
B 埋土Ac1 粘性土Am1 粘性土As1 砂Am2 粘性土
As2-U 粘性土Av 砂
Ac2-L 粘性土As2 砂Dc1 粘性土Dg1 砂礫
B 埋土Ac1 粘性土Am1 粘性土As1 砂Am2 粘性土Ac2-U 粘性土Av 砂
Ac2-L 粘性土As2 砂Dc1 粘性土Dg1 砂礫
0.80
3.14.6
8.09.4
17.2
23.0
24.4
30.0
深さ(m) N値0 10 20 300 10 20 30
B
Ac1Am1
Dg1
Am2
As1
As2
Ac2-L
Av
Ac2-U
Dc1
B 埋土Ac1 粘性土Am1 粘性土As1 砂Am2 粘性土
As2-U 粘性土Av 砂
Ac2-L 粘性土As2 砂Dc1 粘性土Dg1 砂礫
B 埋土Ac1 粘性土Am1 粘性土As1 砂Am2 粘性土Ac2-U 粘性土Av 砂
Ac2-L 粘性土As2 砂Dc1 粘性土Dg1 砂礫
0.80
3.14.6
8.09.4
17.2
23.0
24.4
30.0
深さ(m) N値0 10 20 30
B
Ac1Am1
Dg1
Am2
As1
As2
Ac2-L
Av
Ac2-U
Dc1
B 埋土Ac1 粘性土Am1 粘性土As1 砂Am2 粘性土
As2-U 粘性土Av 砂
Ac2-L 粘性土As2 砂Dc1 粘性土Dg1 砂礫
B 埋土Ac1 粘性土Am1 粘性土As1 砂Am2 粘性土Ac2-U 粘性土Av 砂
Ac2-L 粘性土As2 砂Dc1 粘性土Dg1 砂礫
0.80
3.14.6
8.09.4
17.2
23.0
24.4
30.0
深さ(m) N値0 10 20 300 10 20 30
B
Ac1Am1
Dg1
Am2
As1
As2
Ac2-L
Av
Ac2-U
Dc1
B 埋土Ac1 粘性土Am1 粘性土As1 砂Am2 粘性土
As2-U 粘性土Av 砂
Ac2-L 粘性土As2 砂Dc1 粘性土Dg1 砂礫
B 埋土Ac1 粘性土Am1 粘性土As1 砂Am2 粘性土Ac2-U 粘性土Av 砂
Ac2-L 粘性土As2 砂Dc1 粘性土Dg1 砂礫
0.8 B
Ac1
埋土
粘性土
Am1
As1
Am2
Ac2-U
Av
Ac2-L
As2
Dc1
Dg1
粘性土
砂
粘性土
粘性土
粘性土
粘性土
砂
砂
砂礫
Clay
Clay
Clay
Sand
Clay
Clay
Sand
Clay
Sand
ClayGravel
Depth (m) N-value Fig. 9 Soil profile at the site for FEM
Table 1. Soil parameters for FEM
Proceedings of the First International Conference on Press-in Engineering 2018, Kochi
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図6 盛土中央地盤沈下量比較Fig. 11 Comparison of ground settlements
(d) Ac2-L layer
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(b) Ac2-U layer
(c) Ac2-L layer
(d) As2 layer
図7 盛土中央直下地盤
過剰間隙水圧比較
Fig. 12 Comparison of excess pore water pressures
150m
34m
32m
Fig. 10 3D FEM modeling
Boundary conditions:
Y-Z plane: X-direction fix,
Drain condition
Z-X plane: Y-direction fix
Undrain condition
Bottom plane: X, Y, Z-directions fix
Undrain condition
Z Y
X
Proceedings of the First International Conference on Press-in Engineering 2018, Kochi
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how much the lateral displacement at the toe of
embankment and this allowable value has to be
determined to generalize this PFS method. And one more,
as many of engineers concerned, the behavior during
earthquake is important, especially in Japan. Therefore,
the confirmation of performance under earthquake
should be examined. Those should be the next target for
the PFS method.
5. Acknowledgements
As mentioned in this paper, the development of PFS
method was done under the research group of PFS
method whose chair was Professor Emeritus of Kyushu
University, Hidetoshi Ochiai. The authors would like to
give their sincere gratitude to all the members of this
committee for their enormous efforts to develop this
method.
References
PFS Method Technical Manual. 2005. Technical
Committee of PFS Method, JASPP, Japan. (in
Japanese)
Nakai, T. 2013. Constitutive modeling of geomaterials
-Principals and applications-. CRC Press.
Gro
und
dep
th (
m)
Lateral flow (mm)
0
5
10
15
20
25
30
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25
20
15
10
5
00 20 40 60 80100120
30
Observation
Analysis result
Fig. 13 Lateral displacement at the
toe of embankment
